1. Field of the Invention
The present invention relates to an apparatus for detecting the three-dimensional configuration of an object employing an optical cutting method.
2. Description of the Related Art
FIG. 5 schematically shows a conventional apparatus for measuring the three-dimensional configuration of an object by an optical cutting method. The apparatus includes a laser source 1 and a rotary mirror 3 disposed ahead of the laser source 1, with a cylindrical lens 2 disposed therebetween. An object 4 to be measured is placed ahead of the rotary mirror 3. An image sensor 5 is disposed in opposition to the object 4. A determination section 6 is connected to the image sensor 5, and a memory section 7 is connected to the determination section 6. The apparatus further includes an optical lens 8 for forming an image of the object 4 on the image sensor 5, which is disposed between the object 4 and the image sensor 5.
An optical detector 9 is disposed in the vicinity of the rotary mirror 3 in order to detect a reference angle of the rotary mirror 8. A counter 10 is connected to the optical detector 9, and the output of the counter 10 is connected to the memory section 7 via a data bus 11. A data processor 13 is connected to the memory section 7 via a data bus 12.
The image sensor 5 has a plurality of pixels 5a which are arranged on an X-Y plane when the axis connecting the image sensor 5 and the object 4 is assumed to be a Z axis. The determination section 6 and the memory section 7 have a plurality of comparators 6a and a plurality of memories 7a, respectively, which are arranged in one-to-one correspondence with each of the pixels 5a of the image sensor 5.
The conventional apparatus having the above-described construction operates in the following manner. A laser beam is radiated from the laser source 1 and, simultaneously, the rotary mirror 3 is rotated about the Y axis at an angular velocity .omega.. The laser beam radiated from the laser source 1 is diverged in the direction of the Y axis by the cylindrical lens 2, and it is then reflected by the rotary mirror 3, whereupon it forms a slit-shaped beam 14. The beam 14 rotates at the angular velocity .omega. as the rotary mirror 3 rotates. When the beam 14 passes through the optical detector 9, a detection signal is output from the optical detector 9 to the counter 10. Upon receiving this signal, the counter 10 starts to measure time. Thereafter, time data indicative of the time t reached every moment is momently output from the counter 10 to the memory section 7 via the data bus 11.
When the rotary mirror 3 further rotates and the slit-shaped beam 14 irradiates the object 4, the beam 14 scans the surface of the object 4 as the beam simultaneously forms an optical cutting line 15 on the surface of the object 4. At this time, an image 16 of the optical cutting line 15 is projected onto the image sensor 5 through the optical lens 8. Each comparator 6a of the determination section 6 makes a determination on the basis of an output signal from the corresponding pixel 5a of the image sensor 5 as to the passage of the image 16 of the optical cutting line 15 through the corresponding pixel 5a. When each comparator 6a determines that the image 16 of the optical cutting line 15 has passed the corresponding pixel 5a, the comparator 6a outputs a trigger signal to the associated memory 7a of the memory section 7, whereby the time data that is on the data bus 11 at this time is stored in the memory 7a.
When items of data which are each indicative of the time t reached at the time of the passage of the image 16 of the optical cutting line 15 through each of the pixels 5a have been stored into the corresponding memories 7a in this way, these items of data, each indicative of the passage time, are read by the data processor 13 via the data bus 12. Because the angle .alpha. by which the slit-shaped beam 14 deviates from the reference angle at a time t reached is expressed by: .alpha.=.omega.t, it is possible to express the beam 14 in the form of a plane equation in which the time t reached is used. Furthermore, a point on the image 16 projected on the image sensor 5 corresponds to one point on the surface of the object 4, and these points are positioned on the same line passing through the center of the optical lens 8. Therefore, from the equation expressing this line and a plane equation expressing the beam 14, the spatial coordinates of a certain point on the object 4 which corresponds to one point of the image 16 being projected on the image sensor 5 are calculated. The configuration and the position of the object 4 are calculated by the data processor 13 employing the above-described method.
However, the following problem is encountered in the event that any noise or flash which involves a sudden change in the degree of brightness and darkness enters one or more pixels 5a, or in the case where the background of the object 4 is extremely bright. In such cases, each pixel 5a detects the image 16 of the optical cutting line 15 with a reduced S/N ratio, thereby leading to a reduction in the level of precision with which the three-dimensional configuration of the object 4 is measured.